The present invention relates to a delay circuit for an interior light of a motor vehicle.
The circuit of the interior light of a motor vehicle is usually so designed that it extinguishes immediately when door contacts associated with the doors of the motor vehicle are opened. This has the consequence that the driver finds himself in darkness after getting into the vehicle as well as when the driver leaves the vehicle.
To avoid this deficiency, a delay circuit is disclosed in U.S. Pat. No. 3,221,211. In this disclosure a set of door contacts, through a monostable multivibrator, switches a light source which continues to light for some time after the opening of the motor vehicle door. The circuit disclosed in U.S. Pat. No. 3,221,211 is not readily suitable for application to the circuit, usually provided in a motor vehicle, of the interior light. Either the wiring of the existing light would have to be changed, while the usual function thereof would then be lost, or an additional light would have to be provided.
U.S. Pat. No. 4,071,805 discloses a delay circuit for the interior light of a motor vehicle, in which delayed switching-off of the light after closing of a set of door contacts is attained by means of a series connection of the door contacts, a switching amplifier and a relay winding, the delay time being provided by a resistance-capacitance network in parallel with the switching amplifier, and the relay winding actuates a switch parallel to the door contacts. Apart from the fact that the use of a relay makes the circuit expensive, it is a disadvantage in the case of U.S. Pat. No. 4,071,805 circuit must be connected to at least three poles of the vehicle power supply.
U.S. Pat. No. 3,916,250 discloses a delay circuit for the interior light of a motor vehicle, in which the delay function is initiated not by means of their door contacts, but by means of additional contacts mounted at the handle of the vehicle door. This enables the interior illumination to be switched on before getting into the vehicle. This circuit also operates with a relay and requires three connections as well as the additional switching contacts.